Edmodo BB#1 - Persistent Input Validation Vulnerability

Document Title:
===============
Edmodo BB#1 - Persistent Input Validation Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1921


Release Date:
=============
2016-08-22


Vulnerability Laboratory ID (VL-ID):
====================================
1921


Common Vulnerability Scoring System:
====================================
3.3


Product & Service Introduction:
===============================
Edmodo is a global education network that helps connect all learners with the people and resources needed 
to reach their full potential. Edmondo is part of an official security disclosure program.

(Copy of the Vendor Homepage: https://www.edmodo.com/about )


Abstract Advisory Information:
==============================
The vulnerability laboratory core research team discovered a persistent input validation vulnerability in the Edmodo online service web-application.


Vulnerability Disclosure Timeline:
==================================
2016-08-29:	Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Affected Product(s):
====================
Edmodo
Product: Edmodo - Online Service (Web-Application) 2016 Q3


Exploitation Technique:
=======================
Remote


Severity Level:
===============
Low


Technical Details & Description:
================================
The persistent input validation vulnerability has been discovered in the official Edmodo online service web-application.
The security vulnerability allows remote attackers to inject own script code on the application-side of affected modules.

The vulnerability is located in the placeholders `Title of the web page` - http:// or embed fields in the `Note` and 
`Assignment` sections. Remote attackers with low privilege web-application user accounts are able to inject own malicious 
script code via GET method request. The vulnerability is located on the application-side of the vulnerable service module.

The security risk of the vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.3. 
Exploitation of the persistent input validation web vulnerability requires a low privileged web-application user account and 
low or medium user interaction. Successful exploitation of the vulnerability results in session hijacking, persistent phishing 
attacks, persistent external redirects to malicious source and persistent manipulation of affected or connected application modules.

Request Method(s):
						[+] GET

Vulnerable Service(s):
						[+] www.edmodo.com
						
Vulnerable Module(s):
						[+] Home


Proof of Concept (PoC):
=======================
The xss web vulnerability can be exploited by remote attackers with low privileged user account and low user interaction.
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.


Manual steps to reproduce the vulnerability ...
1. Create an account in the web-application to access with low privileges
2. Go to the `share link` by function
3. Create in the `title of the web page` `http;// or <embed>`  input a script code payload  
Note: `<img/src=` onerror=alert(document.cookie)>
4. Click the button
5. Now, the payload executes on edit and can be posted via share function
6. Successful reproduce of the remote cross site scripting vulnerability!


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure parse and encode of the vulnerable input fields. Restrict the input and disallow usage of special chars.
Filter and setup a secure exception handling that prevents the persistent execution in the output location.


Security Risk:
==============
The security risk of application-side input validation web vulnerability in the Edmodo web-application is estimated as medium. (CVSS 3.3)



Credits & Authors:
==================
Vulnerability Laboratory [Research Team] - SaifAllah benMassaoud (http://www.vulnerability-lab.com/show.php?user=SaifAllahbenMassaoud ) 


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=========================
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